For fixing a magnet to a rotor core of a rotor to be used in a motor, there is a method of fixing the magnet to the rotor core with resin. One of such techniques of fixing the magnet with resin is disclosed in for example JP2001-298887A. In this technique, as shown in FIGS. 20 and 21, a rotor 101 is configured such magnets 111 are fixed to a rotor core 112 with resin supplied between adjacent ones of the magnets 111. FIG. 20 is an external perspective view of the rotor 101 disclosed in JP2001-298887A. FIG. 21 is an exploded perspective view of the rotor 101 in which resin 113 has not been injected yet.
In the above prior art, however, even though both end portions of each magnet 111 in a circumferential direction are fixed with resin, a central portion 111a of each magnet 111 in the circumferential direction is not fixed with resin. Stress by a centrifugal force generated by rotation of the rotor 101 is therefore liable to concentrate on resin portions existing in both end portions of each magnet 111 in the circumferential direction. Accordingly, the magnet 111 is retained insufficiently with resin and thus may fall out of the rotor core, 112 which may be broken by stress concentration.
To prevent the above defects, a rotor 201 shown in FIG. 22 is provided. FIG. 22 is a sectional view of a hollow cylindrical rotor core 212 made of laminated electromagnetic steel sheets, viewed in a radial direction thereof. This rotor 201 is also configured such that magnets 211 are fixed to the rotor core 212 with resin 213. Specifically, as shown in FIG. 22, a plurality of slots 212s is arranged at predetermined pitches in a circumferential direction. Each slot 212s is a through hole for insertion of the magnet 211 in the rotor core 212. Molten resin 213 is supplied into each slot 212s from each cylinder and is solidified in each slot 212s, fixing the magnet 211. Thus, the magnet 211 could be prevented from fall out of the rotor core 212.
However, if it is insufficient to control the amount of resin 213 to be filled, some portions unfilled with resin 213 may be formed and the filling amount of resin 213 may become different by site, and so on. In this case, the positions of the magnets 211 in each slot 212s are liable to vary from slot to slot, resulting in a large unbalance amount of the rotor.
Even if the filling amount of resin 213 is sufficiently controlled, the positions of the magnets 211 in each slot 212s are not controlled at all. Mere sufficient control of the filling amount of resin 213 is likely to cause different positions of magnets 211 between slots 212s and thus increase the rotor unbalance amount. Until now, actually, no consideration has been given to the arrangement (fixing) positions of the magnets 211 in each slot 212s in the rotor 201 shown in FIG. 22.
For fixing the magnets 211 in each slot 212s with resin 213, as mentioned above, the molten resin 213 is supplied into each slot 212s from each cylinder. Therefore, the resin has to be charged into a number of cylinders, which is low in work efficiency.